balsillie



(Eri '16 i923.

J. G. BALSLLIE REFLECTOR FOR USE 1N LIGHT PRoJEcToRs Filed Feb. l5, l

3 Sheets-Sheet l 0t.1e,1923. 1,470,793 J. G. BALSILLIE RBFLECTOR FOR USEIN LIGHT PROJECTORS Filed Feb. 15, 1923 5 Sheets-Sheet 2 Oct. 16, 1923.v 1,470,798

J. G, BALslLLlE REFLECTOR FOR USE IN LIGHT PROJEQTORS Filed Feb. v151925 3 Sheets-Sheet 3 Jaim Ti/Maille,

Patented Get. 16, 192,3.

UNI-TED STATES 1 JOHN G. BALSILLIE, MELBOURNE, .AUSTRALIA.

REFLEGTOR FOR USE IN LIGHT PROJECTORS.

'Application ied'rebruary i5, 1923. seriai No. 619,225.

To 'all 'whom t may concern.'

Be it known that I, JOHN G. BALSILLIE, a. subject of the King of GreatBritain, residing at Melbourne, Australia,` have invented Vcertain newand useful Improvements in Reflectors for Use in Light Projectors, ofwhich Ithe Vfollowing' is a specification.

This invention relates to reflectors and has'for its object theproduction of a beam of light which in cross section has the shape of anelongated ellipse considerably wider in the middle than at its ends `andwith the rays of light Vconcentrated to a beam, said beam having acontour of equal intensities in the shape approximately of an isoscelestriange, and wherein the maximum light intensity is positioned in a zoneoccupying the middle of the triangle such as is required by many Statestatutes relating to motor vehicle headlamps.

Another object of the invention is to produce a surface which, whilemade up of a number' of meeting surfaces of different curvatures will befree of sharp grooves which interfere with the bufling productionprocess.

)ino-thor object of the invention is to produce a reflector having asnearly a stigrnatic surface'of revolution as possible to facili- :zotate manufacture and cheapen production.

lilith these and other objects in view which will appear as thisspecification proceeds. in v invention will be descrilied in connectionwith the accompanying drawing in which:

Figure l is a diagrammatic front view of my reflector showing the-wedge-shaped Zones or surfaces and also that the planes passing throughthe edges of the zones or surfaces converge `to asmall area on one sideofthe reflector;

Fig. 2 is a diagrammatic view of a modified Aconstruction wherein theZones or wedgeshaped surfaces comprising the upper and `lowerparts ofthe reflector taper in opposite directions from a plane passed throughthe horizontal diameter of the reflector;

Fig. 3 represents second modification; `Figs. l and- 5 representmodifications wherein the wedge-shaped surfaces only comprise a portionof the entire surface of the reflector. a relatively small portion be--ing a stigmatic surface ofrevolution;

AFig; 6 is a graphic representation of two tapered surfacesillustratingthat the boundlocated beyond the reflector.

ing edges ofeach surface areof different oblique sections of the samestigmatic surface of `revolution and also giaphicall;v Y

showing that `the elements of the` surface of each section converge ondifferently posi- 4tioned loci Fig. 7 is a. diagrammatic representationof the shape of light areas of uniform light intensities required bymany State statutes and relative intensities of illuminationapproximated by applicants reflector;

Fig. 8 is a diagrammatic representation of a cross section of thevarious beams projected by the several surfaces comprising.

the left half of the reflector shown in Fig. 9; Fig. 9 is an enlargedview ofgmy reflector; Fig. l0 is a section of the reflector shown inFig. 9 on the line lO-lO thereof.

Tlie'laws of many States require that the quantity of light projected bytwo motor vehicle head lights must be substantially that indicated inFig. 7, the contour lines lioining points of equal light intensity atl0() feet distant from the head lights when a light Source of 2l candlepower is positioned at the focal point of each reflector, the valuesbeing in apparent candle power. 4

My present invention has7 therefore, primarily for its object theprovision'of a reflector which will project a beam of' light; the crosssection of which will be as hereinbefore specified. Such lightdistribution as occurs beyond the legally specified area is designed toutilize the excess light to the best advantage, but the lightdistribution wit-hin the specified area will of course be in accordancewith requirements.

I accomplish this object by distorting a surface of revolution of aconie section into a number of wedge-shaped surfaces A, A, A3, etc.,each surface being' bounded bv planes which diverge from a Small area Ppositioned on or about a plane C passed through the axis D of thereflector T.

The bounding edges F of each wedgeshaped surface A,` A2, A3, ete., con`form to the surface of revolution of the same conic section. Theelements G, Fig. 6 of each wedge-shaped surface A, A2, A3,

etc.7 are preferably straightyand these elements converge to differentlypositioned loci H and H', etc. These loci are always AS shown in .Figythe surfaces arepdistorted from surfaces of lrevolution andare so shapedthat Ill) vSuch portionsof the retiector sur Y of the curvature of thesurface ot revolu- Afaces A', 112,113, etc., radiates from loci ll,

H, etc., positioned beyond the retiector, and at the same timemaintaining at the bound-V edgc of each tapered surface the curvaturesof the surface oli revolution, a. resented at F, F etc., is to displaceor site.. the projected beam so that its appar .it axis is asshown at.1x, K1", etc..r F ig. 8 oil" the scctions A', A2, A3, etc. .The amountof` the skewin'gor displacement ofthe rays ai proximately equal 'to theangle enclosed by the bounding planes, and the arri plano (l, Lace asare tion (shown in Figs. -1 and operate to patch up thedightin the axialcenter oi` the proJected beam.` This `gives the de-A signerfsome`latitude for errors in manip facture.

Sharp angles or meeting lines of sec` tions are `undesirable because oflilliirg,l up 'with buffing powder which is di'i'iicult to re` move,hence the small interspersed sections S, S, etc., have considerableproduction advantages. These interspersed suriaees may not be alwayssutlicient for the desiired patching `up in which case designs as shown`at U` in Figs. 4 and 5 may then be resorted to.

' It should be clearly understood that the light pattern shown in Fig. 7is merely a graphic representation oi the light dis-- tributionspecified by the law.

The reflectors are nearly stigmatic in shape and consequently thegeneral form of the area theyv illuminate will be the same ellipticalshape'. However, the distribution of the lightl within this areal willvary somewhat but may be caused to stay within the prescribed limits. Byvaryingthe position of the loci H, H of the designs shown in Figs. 2, 3,4 or 5 I may malte the contour of each surface A', A2, A3, etc., projecta beam of light so that the `light distribution in the illuminated areais substantiallyv7 the same as that projected by the design shown inFig. 1.

`T he tables appended' apply to the hyperbola of 6o divergence with 1.22inch Jfocus. I particularly mention h perbola as otherwise muchdifficulty wou d arise in impartin `the requisite curvatureV to theelements ofgeach sectionto'obtain the desired light s read, anddistribution from each section.

he projected light pattern oi each section These are illustrated at tl,Si, ctc.,

A, A?, A3, ctc., will be of the shape as shown at. a. .ff/2tlg,etc.,rFig. 8. `Points of uniform light intensity of, each light atterriVare joined by lines as indicatedfat in Fig. 8. The beam Afrom eachsection is axiallyrdisA placed `an amount dependent upon its location onVthe' reflector surface. Thus the -bcaiu ot light from section A nearestto the rim oit' thereector T. Figure 9, will be displaced as shown at u.Figure 8 and the beam of light ,from A2, Fig. 9 will be displaeedasshown at a? Fig. 8, ete.

1t will thus be seen that the cross secd tion of the lightintensitypattern, the left halt ot which is shown in F ig. 8 when projected by the reflector as a whole will be of a shape which complieswith the lejal tern of light intensity as shown in The law requires thatthe specified pattern of light intensity, Fig. `7 must be achieved bythe location oi a light source of 21 `candle power placed at or aboutthe 'ioeal point of each reflector. It is, there- ,fore at Vall timesyunderstood when the re- 4llector herein described Ais used forrojection of light in an automobile head) lamp that the source of lightot this candle power must be placed at or about the focal'point which is1.22 inches in the specified design,

The following table has been ascertained matheinatically and is usedv toprepare a templet. The surface of a die is then shaped to the curve otthe templet by rotating `the die past cutters until its surface at all`times touches the surface of the templet when the r`templet is axiallypositioned. The various sections as shown in Fig. 9 are then laid off onthe die surface, and the surface ,of each Vof the sections is thenshaped as shown at Gr in Fig. 6. The reflectors are drawn from this dieby any skilled metal worker, but` particularly by a recently develoliied`process which may form the subject ot. a separate application.

lll

a number Q Wedge Shaved Surfw* erranged side by side with the Widerportions all lying on one side of the axis-of the reflector, saidsurfaces having their bounding edges in planes converging to a concen`trated or smallarea at one side of the periph ery of the reflector',each Surface being distorted froina surface of revolution and theelements joining the bounding edges of each surface being Vstraight andthe elements of the different surfaces radiating from differentlylocated loci.

, 2. A concave reflector comprising a nurnber of wedge-shaped surfaces,the bounding edges of which lie in planes which coniferge towards eachother :from one side of the reflectorthrough .the reflector to the otherside thereof and which meet in aconcentrated or sniall area beyond theperiphery of the reflector, each surface being distorted from a surfaceof revolution and the elements joining the bounding edges of cachsurface being straight lines and the elements of the dierent surfacesradiating from differently located loci.

3. A concave reflector comprising a num` er of Wedge-shaped surfaceslying in substantially the saine direction, said surfaces having theirbounding edges in planes con` verging to a concentrated or small area atone side of and beyond the periphery of the reflector, and narrow stripslying between adjacent Wedge-shaped surfaces, said strips being sectionsof a stigmatic surface of revolution as described.

4f. A concave reflector symmetrical with respect to a vertical planepassed through the axis of the reflector, and including a number ofWedge-shaped surfaces, the bounding edges of the surfaces being inplanes which converge from the Widest portion of each surface to saidfirst mentioned plane, and rneet the saine in lines entirely outside theperiphery of the reflector, each surface being distorted from a surfaceof revolution and the elements joining the bounding edges of eachsurface xbeing straight lines andthe elements of each of the differentsurfaces radiating from differently located loci.y

5. A. concave reflector' symmetrical With respect to a vertical planepassed through the axis of the reflector and including a number ofWedgeshaped surfaces, the bounding edges of the surfaces being in planeswhich converge frornthe Widest Vportion of the surfaces to said firstmentioned plane and meet the saine in lines entirely outside of theperiphery of the reflector, and narrow strips lying between adjacentwedge-shaped surfaces, said strips being sections of a stigmatic surfaceof revolution;

6.`A reflector having the general shape of a surface of revolution of aconic section, said reflector including tapered sections or zones lyingside by side and extending frein one edge of the reflector to` theother, each tapered surface or zone being distorted from a surface ofrevolution and the elements which generate the respective taperedsurfaces or zones and which join the opposite edges of these surfaces orzones radiating from differently located l'oci.

7. A reflector having the general shape of a surface of revolution of aconic section, said reflector including sections or zones, the boundingedges ofwhich lie in the surface of revolution, the respective surfacesof which are distorted from the surface of revolution and the elementswhich generate said surfaces or zones and Which join the opposite edgesof these sections or zones radiating from differently located loci, andnarrow strips lying between adjacent sections or zones, said stripsbeing sections of a stigmatie surface of revolution.

In testimony whereof I' hereunto affix iny signature.

p JOHN G. BALSILLIE.

